The number of people who are being actively monitored for Ebola in New York has tripled to 357 people, none of whom has displayed any symptoms, city health officials announced Wednesday.

The vast majority of those being monitored arrived in New York in the last 21 days from West Africa, the New York City Health and Hospitals Corporation said in a statement. Those under monitoring are being checked out of "an abundance of caution," the statement said.

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The latest announcement comes as Ohio said it was officially Ebola-free and Texas prepared to end its observation period for the last 27 healthcare workers. The Texas group will complete its 21-day monitoring period on Friday, according to state officials.

The Ohio Department of Health reported that the state had officially moved to "triple-zero" status: no confirmed cases of Ebola, no people under quarantine, and no contacts with any possible Ebola patients.

Ebola is suspected in almost 5,000 deaths in Liberia, Sierra Leona and Guinea. More than 13,000 cases have been reported in eight affected countries, including the United States.

Nine people have been treated in the U.S. for Ebola, including Thomas Eric Duncan, a Liberian who died last month. One doctor, Craig Spencer, remains hospitalized in stable condition in New York.

Many Americans first became attuned to the worst Ebola outbreak in history over the summer, when medical missionaries returned after contracting the virus in West Africa. Americans saw televised glimpses of isolation suits as the patients returned to the United States.

Nancy Writebol and Dr. Kent Brantly were treated in Emory University Hospital in Atlanta and released on Aug. 19 and Aug. 21, respectively. Dr. Rick Sacra was discharged from Nebraska Medical Center on Sept. 25.

Texas officials quarantined about a dozen of Duncan's friends and relatives, including his fiancee, and ordered dozens of other people to be confined and monitored. None contracted Ebola.

But two nurses who were involved in Duncan's treatment were infected with Ebola. One flew on an airplane to visit Ohio and then back home to Texas before she knew she had the virus, prompting hundreds of people on the flights — or who used the plane on other flights before it was taken out of service — to go into some form of monitoring or counseling.

Both of the nurses, Nina Pham and Amber Vinson, are now free of Ebola and have returned to Texas after being treated at specially equipped hospitals in Maryland and Georgia.

Another healthcare worker involved in Duncan's care traveled on a cruise ship, but her tests proved negative for Ebola. However, the ship was not allowed to dock in Mexico because officials there feared the virus, even though the woman was not symptomatic.

michael.muskal@latimes.com

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